The present invention relates to methods for enhancing steam turbine power plant efficiencies, and more particularly, to a method which governs the adjustment of the throttle pressure of a steam turbine to optimize the efficiency thereof with respect to the thermodynamic operating conditions at desired loading conditions of the power plant.
During the operation of a steam turbine in a power plant facility, the steam pressure drops existing across the modulating steam admission valves of the steam turbine cause compositely throttling losses in efficiency of the steam turbine which eventually renders a reduction in the effective energy produced by the power plant. Control systems, like the ones disclosed in the copending U.S. Patent application Nos. 889,770 and 889,764 (referenced hereabove), for example, have been proposed to minimize the valve throttling losses by governing the adjustment of the throttle pressure of the turbine in accordance with a set of predetermined optimum valve position characterizations which are generally preprogrammed therein. However, the optimum valve position points do not necessarily provide under all conditions, the optimum thermodynamic operating points of the steam turbine which, in most cases, cannot be determined a priori.
For example, thermodynamic parameters, like pressure and temperature, of the steam turbine of a power plant have a tendency to vary, under a substantially fixed electrical loading state, in time, as a result of changing environmental factors or the like. As a result, the optimum valve position points which may have been predetermined for one set of thermodynamic conditions may not optimize the efficiency of the steam turbine thermodynamically at substantial steam temperature and pressure variations from the one set. Apparently then, optimizing turbine efficiency with respect to throttling losses does not necessarily additionally guarantee an optimum in thermodynamic operation of the steam turbine. It appears that it may also be necessary, for the purposes of optimizing the efficiency of the steam turbine thermodynamically, to compensate for the variations in the steam temperature and pressure of the steam turbine during the normal operation thereof. Accordingly, a method capable of compensating for these changing thermodynamic conditions appears most desirable with regard to further improving the energy production efficiency of the steam turbine power plant.
Along the same lines, it is well known that for a given turbine loading condition, the maximum turbine efficiency is actually reached with minimum steam flow through the turbine. It seems to follow that measuring the steam flow through the turbine may be a step in the direction of establishing when a steam turbine is being optimally operated at a desired plant loading condition. However, known steam flow measuring devices do not appear to offer the sensitivity required for efficiency control purposes probably because a majority of these instruments use a differential steam pressure measurement in their derivation of steam flow. In an experiment with one of these known type flow measuring instruments, a deviation of approximately 0.3% in flow values are measured for a constant steam flow. Apparently, if steam flow is to be the turbine parameter which reflects efficiency under varying thermodynamic conditions, then a method, other than direct measurement, is required to provide a more accurate and precise measurement thereof.